1. Field of the Invention
The present invention relates to a cartridge assembly, and in particular to a cartridge assembly of a projectile for a large-bore gun or a tank-mounted gun.
2. Description of the Related Art
A typical cartridge assembly for a large-bore gun has a cylindrical casing for enclosing the cartridge components, which is made of metal or a combustible material, with a cupped breech end. Fitted over the cupped breech end is a heavy steel stub case, with a rubber gasket to provide a pressure seal between the stub case and a gun barrel. Metal priming tubes filled with a combustible substance extend from an opening in the breech along an entire length of the casing. A propellant charge material is provided in the casing, loaded through an opening in the side of the casing. An igniter head is threaded through a hole in the stub case base, penetrating the cupped breech of the casing to ignite the priming tubes. An open mouth cavity is provided at the forward end of the casing for insertion of an after end of the projectile. The open mouth of the casing is securely affixed to an obturator of the projectile through a number of conventional means, including crimping or cementing.
Several shortcomings have been identified with such a cartridge assembly. Newer projectiles are physically longer and project farther into the casing, requiring use of shorter metal priming tubes. Use of a shorter priming tube has resulted in incomplete ignition of the propellant charge, thereby resulting in uneven pressure changes in the casing produced by incomplete propellant burn, and an erratic pressure differential (.DELTA.P) between the breech and mouth of the casing. Such uneven pressure changes result in erratic motion and balloting of the projectile during its travel down the barrel of the gun, and excessive yaw of the shell after it emerges from the barrel. In a worst case, an excessively large .DELTA.P (normally 3% to 10% of maximum pressure) can result in deformation of the projectile.
Holes in the typical non-combustible priming tubes are provided for transmitting the ignition spark inside the tube to the propellant. However, if the propellant has settled unevenly in the casing, and an air pocket has formed in the location of a hole, the propellant around that air pocket will not be ignited, further adding to uneven burning of the propellant.
A further shortcoming associated with the prior art is that typical non-combustible priming tubes cannot be used with a double case projectile, having two adjoining casings loaded with propellant, for use in a large-bore gun having a longer than standard chamber. In such a projectile, separate priming tubes with separate igniters are required for each casing. Because of the sequential firing of the holes in the priming tubes, propellant in one casing ignites before the propellant in the other casing. Such non-simultaneous ignition can result in a significant .DELTA.P which can damage the projectile, or at least result in erratic motion and balloting of the projectile.
A further shortcoming associated with the prior art is the use of the heavy steel stub case, which is expensive to manufacture and difficult to manipulate during gun operations.
A further shortcoming associated with the prior art is the means used to affix the obturator to the casing. Cemented and crimped seals frequently fail during drop tests, so the propellant must be loaded into the casing in bags, in order to prevent propellant grains from spilling out of the casing Propellant loaded in this fashion is further susceptible to uneven loading and uneven burn.
A further shortcoming of the prior art is identified in the manner its design dictates loading the propellant. Because no large opening exists in the casing, the propellant is loaded by hand, in very small amounts. This operation is tedious and time-consuming.